As circuit geometries shrink to ever smaller feature sizes, lower deposition temperatures may be preferred for depositing Si and SiGe films, for example due to introduction of new materials into semiconductor devices and the requirement for reduction of thermal budgets of shallow implants in source and drain regions. Moreover, it is evident that Si-containing films having a blanket coverage of a substrate and such films having patterned coverage of a substrate will be needed for future devices. Currently, Si-containing films having patterned coverage are provided through selective deposition wherein different deposition characteristics are present on different substrate materials. For example, some Si-containing gases deposit Si films on Si surfaces but not on oxide and nitride surfaces.
However, such selective deposition typically requires a substrate temperature above about 700° C. Due to reduced thermal budgets noted above, it is desirable for many applications to deposit Si-containing films at substrate temperatures below about 700° C. However, deposition selectivity may be lost at these low substrate temperatures, and unintended non-selective deposition can result over the whole substrate including any structures formed on the substrate. This blanket coverage of the substrate makes necessary additional lithography and etch steps to remove the film from the unwanted areas of the substrate to form the desired pattern. These additional steps reduce throughput and increase the expense of forming patterned Si containing layers.